Method and apparatus for filtering a clock signal

Abstract

A method and an apparatus are provided for filtering a substantially square wave signal. At least a portion of the substantially square wave signal is applied to a first filter adapted to pass a range of frequencies adjacent the fundamental frequency and produce a first filtered signal. At least a portion of the substantially square wave signal is also applied to a plurality of second filters, where each of the second plurality of filters is adapted to pass a range of frequencies adjacent an odd harmonic component of the fundamental frequency and produce a second filtered signal. The first signal and the plurality of second filtered signals are combined to produce a representation of a square wave signal having a frequency substantially corresponding to the fundamental frequency.

1. A method for filtering a signal having a fundamental frequency, comprising:
 filtering at least a portion of the signal to pass a range of frequencies adjacent the fundamental frequency to produce a first filtered signal;  
 filtering at least a portion of the signal to pass a range of frequencies adjacent an odd harmonic component of the fundamental frequency to produce a second filtered signal; and  
 combining the first and second filtered signals to form a periodic signal.  
 
   
   
     2. A method, as set forth in  claim 1 , further comprising filtering at least a portion of the signal to pass a range of frequencies adjacent another odd harmonic component of the fundamental frequency and produce a third filtered signal, and wherein combining the first and second filtered signals further comprises combining the first, second and third filtered signals. 
   
   
     3. A method, as set forth in  claim 1 , wherein combining the first and second filtered signals to form the periodic signal comprises combining the first and second filtered signals to form a at least one of a clock signal and a square wave signal. 
   
   
     4. A method, as set forth in  claim 1 , further comprising modifying one of the first and second filtered signals to alter a phase relationship therebetween. 
   
   
     5. A method, as set forth in  claim 4 , wherein modifying one of the first and second filtered signals to alter the phase relationship therebetween further comprises modifying one of the first and second filtered signals to reduce a phase differential therebetween. 
   
   
     6. A method, as set forth in  claim 4 , wherein modifying one of the first and second filtered signals to alter the phase relationship therebetween further comprises modifying one of the first and second filtered signals to substantially synchronize the first and second filtered signals. 
   
   
     7. A method, as set forth in  claim 1 , further comprising reducing a phase differential between the first and second filtered signals. 
   
   
     8. A method, as set forth in  claim 1 , further comprising substantially synchronizing the first and second filtered signals. 
   
   
     9. A method, as set forth in  claim 1 , wherein filtering at least a portion of the signal to produce the second filtered signal further comprises modifying at least the portion of the signal used to produce the second filtered signal to reduce a phase difference between the first and second filtered signals. 
   
   
     10. A method, as set forth in  claim 1 , wherein filtering at least a portion of the signal to produce the first filtered signal further comprises modifying at least the portion of the signal used to produce the first filtered signal to reduce a phase difference between the first and second filtered signals. 
   
   
     11. A method, as set forth in  claim 1 , wherein filtering at least a portion of the signal to produce the second filtered signal further comprises modifying at least the portion of the signal used to produce the second filtered signal to alter a phase relationship between the first and second filtered signals. 
   
   
     12. A method for filtering a signal having a fundamental frequency, comprising:
 filtering at least a portion of the signal to pass a range of frequencies adjacent the fundamental frequency to produce a first filtered signal;  
 filtering at least a portion of the signal to pass a range of frequencies adjacent an odd harmonic component of the fundamental frequency to produce a second filtered signal; and  
 combining the first and second filtered signals, wherein filtering at least a portion of the signal to produce the first filtered signal further comprises applying at least a portion of the signal to a crystal having a resonant frequency approximately corresponding to the fundamental frequency.  
 
   
   
     13. A method for filtering a signal having a fundamental frequency, comprising:
 filtering at least a portion of the signal to pass a range of frequencies adjacent the fundamental frequency to produce a first filtered signal;  
 filtering at least a portion of the signal to pass a range of frequencies adjacent an odd harmonic component of the fundamental frequency to produce a second filtered signal; and  
 combining the first and second filtered signals, wherein filtering at least a portion of the signal to produce the second filtered signal further comprises applying at least a portion of the signal to a crystal having a resonant frequency approximately corresponding to the odd harmonic component of the fundamental frequency.  
 
   
   
     14. A method for filtering a signal having a fundamental frequency, comprising:
 filtering at least a portion of the signal to pass a range of frequencies adjacent the fundamental frequency to produce a first filtered signal;  
 filtering at least a portion of the signal to pass a range of frequencies adjacent an odd harmonic component of the fundamental frequency to produce a second filtered signal; and  
 combining the first and second filtered signals, wherein the signal is a clock signal, filtering at least a portion of the signal to pass a range of frequencies adjacent the fundamental frequency further comprises filtering at least a portion of the clock signal to pass a range of frequencies adjacent the fundamental frequency, and filtering at least a portion of the signal to pass a range of frequencies adjacent the odd harmonic of the fundamental frequency further comprises filtering at least a portion of the clock signal to pass a range of frequencies adjacent the odd harmonic of the fundamental frequency.  
 
   
   
     15. A method for filtering a signal having a fundamental frequency, comprising:
 filtering at least a portion of the signal to pass a range of frequencies adjacent the fundamental frequency to produce a first filtered signal;  
 filtering at least a portion of the signal to pass a range of frequencies adjacent an odd harmonic component of the fundamental frequency to produce a second filtered signal; and  
 combining the first and second filtered signals, wherein the signal is a substantially square wave signal, filtering at least a portion of the signal to pass a range of frequencies adjacent the fundamental frequency further comprises filtering at least a portion of the substantially square wave signal to pass a range of frequencies adjacent the fundamental frequency, and filtering at least a portion of the signal to pass a range of frequencies adjacent the odd harmonic of the fundamental frequency further comprises filtering at least a portion of the substantially square wave signal to pass a range of frequencies adjacent the odd harmonic of the fundamental frequency.  
 
   
   
     16. A method for filtering a signal having a fundamental frequency, comprising:
 receiving the signal; and  
 filtering at least a portion of the signal to pass a first range of frequencies adjacent the fundamental frequency and a second range of frequencies adjacent an odd harmonic component of the fundamental frequency to form a periodic signal.  
 
   
   
     17. A method, as set forth in  claim 16 , wherein filtering at least a portion of the signal comprises applying at least a portion of the signal to a filter adapted to pass the first range of frequencies adjacent the fundamental frequency and a second plurality of ranges of frequencies adjacent a plurality of odd harmonic components of the fundamental frequency. 
   
   
     18. A method for filtering a signal having a fundamental frequency, comprising:
 receiving the signal; and  
 substantially attenuating frequencies outside of a first narrow range of frequencies encompassing the fundamental frequency, and frequencies outside of a second narrow range of frequencies encompassing an odd harmonic component of the fundamental frequency to form a periodic signal.  
 
   
   
     19. A method, as set forth in  claim 18 , wherein substantially attenuating frequencies further comprises substantially attenuating frequencies outside of a first narrow range of frequencies encompassing the fundamental frequency, and frequencies outside of a plurality of second narrow ranges of frequencies encompassing a plurality of odd harmonic components of the fundamental frequency. 
   
   
     20. An apparatus for filtering a signal having a fundamental frequency, comprising:
 means for filtering at least a portion of the signal to pass a range of frequencies adjacent the fundamental frequency and produce a first filtered signal;  
 means for filtering at least a portion of the signal to pass a range of frequencies adjacent an odd harmonic component of the fundamental frequency and produce a second filtered signal; and  
 means for combining the first and second filtered signals to form a periodic signal.  
 
   
   
     21. An apparatus for filtering a signal having a fundamental frequency, comprising:
 means for receiving the signal; and  
 means for substantially attenuating frequencies outside of a first narrow range of frequencies encompassing the fundamental frequency, and frequencies outside of a second narrow range of frequencies encompassing an odd harmonic component of the fundamental frequency to form a periodic signal.  
 
   
   
     22. A filter, comprising:
 a first component coupled to a source of a signal having a fundamental frequency, the first component being adapted to substantially attenuate frequencies outside of a first narrow range of frequencies encompassing the fundamental frequency and deliver a first filtered signal; and  
 a second component coupled to the source of the signal, the second component being adapted to substantially attenuate frequencies outside of a second narrow range of frequencies encompassing an odd harmonic component of the fundamental frequency and deliver a second filtered signal, wherein the first and second components are coupled to form a periodic signal from the first and second filtered signals.  
 
   
   
     23. A filter, as set forth in  claim 22 , further comprising a third component coupled to the source of the signal, the third component being adapted to substantially attenuate frequencies outside of a third narrow range of frequencies encompassing another odd harmonic component of the fundamental frequency. 
   
   
     24. A filter, as set forth in  claim 22 , wherein the first and second components are coupled in parallel. 
   
   
     25. A filter, as set forth in  claim 22 , further comprising a delay element disposed between the source and the first component. 
   
   
     26. A filter, as set forth in  claim 22 , further comprising a delay element disposed between the source and the second component. 
   
   
     27. A filter, as set forth in  claim 22 , further comprising a delay element adapted to receive one of the first and second filtered signals and modify the received signal to alter a phase relationship between the first and second filtered signals. 
   
   
     28. A filter, as set forth in  claim 27 , wherein the delay element is adapted to reduce a phase differential between the first and second filtered signals. 
   
   
     29. A method, as set forth in  claim 27 , wherein the delay element is adapted to substantially synchronize the first and second filtered signals. 
   
   
     30. A filter, comprising:
 a first component coupled to a source of a signal having a fundamental frequency, the first component being adapted to substantially attenuate frequencies outside of a first narrow range of frequencies encompassing the fundamental frequency and deliver a first filtered signal; and  
 a second component coupled to the source of the signal, the second component being adapted to substantially attenuate frequencies outside of a second narrow range of frequencies encompassing an odd harmonic component of the fundamental frequency and deliver a second filtered signal, wherein the first component is a first crystal and the second component is a second crystal.